Common computers provide digital processing in which data are held in positive or negative states (or off and on states) of a device. Digital devices can be semiconducting, magnetic, optical, piezoelectric or other devices. This is referred to as digital computing and it is the economic and technical heart of all current computers, semiconducting devices for computers and computer software. The act of using a digital technology requires that all data must be identified as powers of “2”, this in turn requires that data manipulation, speed, storage, etc that expand at this enormous rate.
This digital route requires significant increases in semiconductor chip size, speed and complexity to accommodate even modest improvements in performance. Semiconductor engineers have responded by making devices smaller and with smaller spacing with larger numbers of devices and ever increasing complexity. The requirements for smaller spacing have pushed the limits of material and photolithography capability and it is estimated that we are reaching the limits of Moores Law (which states that devices will continue to decrease in size and double in capacity every 18 months); in addition, the amount of heat produced by decreasing device spacing is imperiling device performance. The digital computer is rapidly becoming too large and too complex for large number manipulations such as weather analysis, high level encryption, drug discovery, genetic manipulation and many other applications as yet undiscovered because of the limitations on digital computers.
An entirely new type of computer has been proposed which is based on quantum behavior. The spin state of an atom or group of atoms can be manipulated using a number of methods and the spin state can be detected, and/or controllably altered, using an energy source or detector such as an optical source or detector. An atom or atoms with discrete spin states are analogous to a bit in a traditional computer. However, due to the quantum nature of the spin states, a quantum bit (or qubit) can exist in not just one of two states, but also in a superposition of these states. It is this superposition of states which makes it possible for qubit based computers to analyze information at a much greater speed than is possible for traditional computers.
The name Qubit is quite generic in that devices can be made which use (and need to use) only one Qubit whereas others may use many Qubit s. Devices which have been proposed include single Qubit optical amplifiers for encrypted and very high speed messages, multiple Qubit devices for information storage, and multiple Qubit devices for high speed and high density computing. Because the atom can exist in a large number of spin states simultaneously, the interaction of spin states enables a high number of computations with only a small number of atoms. The entire Qubit chip of a supercomputer might well be smaller than a fingernail. In addition, Qubit technology holds promise for combining with optical waveguide technology building high speed optical busses for conventional computers while in creasing encryption capabilities.
Magnetic spin states can be generated in a large number of materials including liquids and solids. However to be useful for a quantum computer, several conditions must be met; 1. The spin state must be capable of being excited; 2. The spin state must be detectable; 3. The spin state must have a lifetime which is long enough to permit the intended calculation to be done and the result to be detected; 4. The device must operate at a practical temperature.
A large number of materials have been proposed for use as Qubit hosts including semiconductors (including quantum dot semiconductors) and superconductors. All of these materials to date have the disadvantage of operation at cryogenic temperatures and or having short spin lifetimes. It has been discovered that the N-V center in diamond had not only the longest spin lifetime of any material but it had this property at room temperature. An N-V center is nitrogen in a substitutional site in diamond which is adjacent to a carbon vacancy. There is an N-V− center with a negative charge, an N-V0 center which is similar but has no charge and a Ns center which is nitrogen substituted for carbon with no adjacent vacancy. The N-V center typically is in one of two charge states, negatively charged N-V− and neutral N-V0.
The N-V center in diamond has several attributes which make it desirable for Qubit based devices. It is easily pumped using low power microwaves. It is also easily detected (emission at 675 nanometers wavelength). Such N-V centers in diamond may have long lifetimes (60 to 500 microseconds) and room temperature operation. Diamond also has a high degree of optical transparency and a high optical index of refraction, enabling construction of optical waveguides and other optical structures.